Materials and processes for rendering the surfaces of articles water, oil, stain and soil resistant are in great demand in industries such as paints and coatings, textiles, paper, construction materials, marine materials, glass and windows, plastics, metals, and many others. Such materials provide protection from wear and dirt and improve the aesthetic qualities and lifetime of industrial and consumer articles. Currently, water, oil, stain and soil resistance is achieved by lowering the surface energy of a material such that water, oil and dirt do not stick to, or wet, the surface of the article. The water and/or oil simply rolls off, or can be easily removed from the article. This is commonly achieved today by applying a fluorochemical or fluoropolymer (such as Teflon) to the surface of an article and is typically done by applying a solution or suspension of the fluorochemical in water, or solvent, and removing the liquid phase by drying. The fluorochemical or fluoropolymer lowers the surface energy and a water and oil resistant coating is obtained.
There is a very serious problem, however, in that fluorochemicals, some materials used in preparation of fluorochemicals, and some decomposition products of fluorochemicals have been shown to be persistent in the environment and have been identified as probable carcinogens by the environmental protection agency (EPA). Further, some fluorochemicals have been shown to be bio-accumulative (the concentration of the chemical accumulates in the human body) and are not removed effectively by the excretion systems of the human body. The environmental and health impact of fluorochemicals and the need to limit their use has been highlighted in several recent publications. [Renner, R. “Tracking the dirty by-products of a world trying to stay clean”, Science, 306, 1887 (2004). EPA Draft Risk Assessment: “On the potential human health effects associated with exposure to perfluorooctanoic acid and its salts”, Jan. 4, 2005. Olsen G. W.; Church, T. R.; Miller, J. P.; Burris, J. M.; Hansen, K. J.; Lundberg, J. K.; Armitage, J. B.; Herron, R. M.; Medhdizadehkashi, Z.; Nobiletti, J. B.; O'Neill, E. M.; Mandel, J. H.; Zobel, L. R. “Perfiluorooctanesulfonate and other fluorochemicals in the serum of American Red Cross adult blood donors”. Environ Health Perspect. 111,1892 (2003). Solomon, G. M.; Weiss, P. M. “Chemical contaminants in breast milk: Time trends and regional variability”. Environ Health Perspect. 110, A339 (2002). Renner, R. “Growing concern over perfluorinated chemicals”, Environmental Science and Technology, 35, 154 (2001) and references therein.] A second, less serious, problem is that fluorochemicals are relatively expensive and costs prohibit their use in many applications.
There is a need for materials, methods and processes for rendering the surfaces of articles water, oil, stain and soil resistant that are not harmful to humans, animals or the environment. There is a need for materials, methods and processes that eliminate or significantly reduce fluorochemical usage in consumer items, while still providing the aesthetic appeal and increased use-life of industrial and consumer items. There is a need to provide such properties at a low cost to allow for their use in common industries.
U.S. Pat. No. 4,617,057 to Plueddeman discloses an oil and water repellent coating composition comprising a blend of an amino-organosilane, a perfluorinated organic compound and a resin selected from the group consisting of a colloidal inorganic based siloxane resin. The siloxane resin comprises an acidic dispersion of colloidal silica and hydroxylated silsesquioxane in an alcohol-water medium. Plueddeman further shows the utility of such compositions for treating clothing fabric such as cotton/polyester blends, see examples 9 and 10. However, the amount of fluorochemical in the treating solutions is 0.9% and 2% (by weight) respectively. Assuming 50% wet pick-up (this is a conservative estimate—most commercial textile treating solutions that are padded onto a textile fabric exhibit a wet pick-up between 60% and 80%) of the solution by the fabric this would correspond to a fluorochemical concentration on the dry fabric of 4,500 and 10,000 parts per million (ppm), respectively. Further, the colloidal inorganic-based siloxane employed is highly hydrophobic and exists as a dispersion in methanol and water. Such dispersions are harmful to the environment, because of their high concentration of volatile organic components (VOC's), and also very expensive.
U.S. Pat. No. 5,908,663 to Wang et al. discloses a method for treating carpets that, in one embodiment, involves applying to the carpet a fluorochemical and a silica colloid. The silica colloid may be used as received, or may be “grated with functional groups or polymers” Column 3, lines 56-57. Wang et al. further shows that the antisoiling properties of the carpet are improved. “Antisoiling” should be distinguished from water and oil repellency; antisoiling refers to the “relative resistance of the treated carpet to dry soiling” under, for example, walk-on conditions. Water and oil repellency refer to the ability of an article (fabric, carpet, textile) to repel liquid stains. Wang et al. shows that the water and oil repellency of the carpet is not improved when colloidal silica is combined with a fluorochemical treatment. When grafted or surface-functionalized silica colloids were employed with a fluorochemical, see Wang examples 80-82, only very poor water repellency values are obtained and most examples failed the oil test. The concentration of fluorochemical on the fabric is typically 1000 ppm (see example 60 and comparison example 40, and other examples in Table 9; 0.1% solids on carpet (SOC) are equivalent to 1000 ppm).
European patent application EP 1 533 356 A1 to Lens provides an aqueous dispersion of a fluorochemical compound, a cationic surfactant and colloidal inorganic particles. The dispersion is applied to textile fabrics such that (page 7, lines 10-12) the “amount of fluorochemical on the substrate is between 0.1 and 3.0% (1,000-30,000 ppm) by weight based upon the weight of the substrate”. It is found (page 3, line 6-7) “the colloidal inorganic particles generally do not negatively impact the oil- and/or water repellency properties that can be imparted on a substrate treated with the composition”.
U.S. Pat. No. 5,760,126 to Engle et al. discloses a water-based coating composition that comprises among other things, a fluorochemical and a colloidal dispersion of surface-functionalized, inorganic microparticles. The surface-modifications of the inorganic microparticle may be achieved using a silane coupling agent which is applied to the particle surfaces at a rate of 1×10−4 to 7×10−3 millimoles per square meter of particle surface area. However, the coatings only provide adequate water repellency and stain resistance when very high levels of fluorochemicals are applied to the substrate (coated article). For example, a fluorochemical loading of 8.1 to 17.7% is required to achieve a contact angle greater than 100 degrees. A contact angle greater than 120 degrees is typically considered to be indicative of good water repellency. Further, the coating compositions employ N-methylpyrrolidone (a material harmful to the environment) presumably as a dispersion aid.
It is desirable therefore to provide a water and oil repellent composition that eliminates or greatly minimizes the need for fluorochemicals in fabric and textile coating formulations. It is desirable to provide such compositions dispersed solely in aqueous coating formulations, without volatile organic components (VOCs) that are harmful to the environment. It is further desirable to provide coating compositions that are durable to washing and do not negatively impact the hand or feel of textiles and garments.